1.2(With reference to two things) to move or cause to move to and fro against each other with a certain amount of pressure and friction: [with object]:many insects make noises by rubbing parts of their bodies together [no object]:the ice breaks into small floes that rub against each other

Origin

The origin of this word is unknown. If you want to impress the consequences of a mistake on someone you may be tempted to rub their nose in it. This comes from house-training puppies or kittens: literally rubbing their noses in any deposit they may make in the house in an attempt to dissuade them from repeating the offence. To rub someone up the wrong way, or irritate them, is another pet-related image, from the idea of stroking a cat against the lie of its fur. Someone pointing out a particular difficulty may say there's the rub. The expression comes from Shakespeare's Hamlet, when Hamlet says: ‘To sleep: perchance to dream: ay, there's the rub.’ In the game of bowls a rub is an impediment that prevents a bowl running smoothly. The same idea is found in the rub of the green, which in golf is an accidental interference with the flight or roll of the ball, such as hitting a tree. More broadly it is also luck or fortune, especially in sport. Rubber, recorded from the mid 16th century, is based on the verb rub. The original sense was ‘an implement (such as a hard brush) used for rubbing and cleaning’. Because an early use of the elastic substance once known as caoutchouc was to rub out pencil marks, rubber acquired the sense ‘eraser’ in the late 18th century. The meaning was subsequently generalized in the mid 19th century to refer to the substance in any form or use, at first often differentiated as India rubber.